XIII PHYLrM CHUllDATA 40.} 



The aortic arch curves over the ri<;lit broiiclius to reach the 

 dorsal body-wall, and then passes directly backwards as the 

 dorsal aorta (d. no.). Owing to the immense size of the pectoral 

 muscles the arteries su])plying them are of corresponding dimensions, 

 and the right and loft iiinominntr iirtcrics (in. a.), from which the 

 carotids (c. c), subclavians {br. ((.), and pectorals {/>r. a.), arise, are 

 actually larger than the aorta itself beyond their origin. In 

 correspondence with the positiqn of the legs, the femoral (/. a.) 

 and sciatic (sc. a.) arteries arise very fai forward : the caudal 

 artery {c.) is naturally small. 



The most characteristic feature in the disposition of the 

 circulatory organs is the almost complete disappearance of the 

 renal 2^ortal sydcm. There are two renal portal veins {r.p.) formed 

 by the bifurcation of tlic caudal ; but each, instead of breaking 

 up into capillaries in the kidney, sends off only a few small 

 branches («. r. v.) which apparently carry blood to that organ, 

 the main vein passing forwards, through the substance of the 

 kidney, and joining the femoral vein {f. v.) from the leg to form 

 the iliac vein (t. v.) whicli, uniting with its fellow of the opposite 

 side, forms the post-caval {pt. c). Tlius the main part, at any 

 rate, of the blood from the caudal and pelvic regions is taken 

 directly to the heart, and not through the renal capillaries as 

 in most Fishes and all Amphibians and Reptiles. 



At the point of bifurcation of the caudal veins a large coccygco- 

 mesenteric vein (c. m. v.) comes off, and, running parallel with the 

 rectum, from which it receives tributaries, joins the portal vein. 

 The abdominal vein of Amphibians and Reptiles appears to be 

 represented, in part at least, by the epigastric vein {cp[j.), which 

 returns the blood, not from the ventral body- wall, but from the 

 great omentum, a fold of peritoneum, loaded with fat, lying ventral 

 to the intestine and gizzard : the epigastric discharges into the 

 hepatic vein. 



The red blood-corpuscles are oval and nucleated. The tempera- 

 ture of the blood is unusually high— over 38' C. (100° F.). 



Nervous System. — The brain (Fig. 1045) completely fills the 

 cranial cavity, and is remarkable for its short, broad, rounded form. 

 The laed'ulkt oUongata {vi. o.) has a well-marked ventral Hexure, as 

 in the Lizard.' The cerebellum (ch.) is of great size, and has a large 

 median portion and two small lateral lobes ovflocculi (/.) ; the surface 

 of the middle lobe is marked by grooves passing inwards in a 

 radiating manner and carrying with them the grey matter, the 

 extent of whicli is thus greatly increased. The metaetde (Fig. 

 1046, v.Ji) is completely hidden by the cerebellum, and the latter 

 is solid, having no epicoele. The hemispheres (c.h.) extend back- 

 wards to meet the cerebellum, and the opile lobes (o. I.) are thereby 

 pressed outwards so as to take up a lateral instead of the 

 usual dorsal position : these are of rounded form, and each 



